Mergers, acquisitions, and employee changeovers have given us a large amount of surplus equipment. After inventorying for accounting purposes and blanking drives we will be donating to the Kramden Institute.

My rack has two APC SmartUPS 1500 RM units installed at the bottom. There are presently four servers plus a tape autoloader and a disk array attached to them, and plans to add two or three servers this year. One server has redundant power supplies, and I'm planning to add redundant PSUs to two of them. The others do not, the future ones may or may not. The problem is every server directly powers from one of the units, and worse, the power cords are long. It's a mess, especially on the floor.

I've read about power distribution units, and if I'm following the idea correctly, you connect a PDU to the UPS and connect servers to the PDU. It also sounds like it's best on the redundant servers to plug one power supply to each UPS, and split the single power servers between the two batteries.

Am I following this right? My goal is to get short power cords for the servers, so I'd prefer a PDU that runs the height of the rack (instead of a 1U rackmounted model), if anyone has any suggestions.

At that most basic level, a PDU is a power bar. Using a basic PDU or power bar you could setup your servers as described as long as should one UPS fail the other could hold the load for a reasonable amount of time.

The next steps up are switched PDU and managed PDUs were you can enable or disable ports as needed during standard operations or power events. These can be very useful, I like to turn off KVMs, monitors, and other unneeded devices if appropriate.

Keep in mind some server PSUs are active passive, where others are active active. This will effect what happens when they are connected between UPSs.

At that most basic level, a PDU is a power bar. Using a basic PDU or power bar you could setup your servers as described as long as should one UPS fail the other could hold the load for a reasonable amount of time.

The next steps up are switched PDU and managed PDUs were you can enable or disable ports as needed during standard operations or power events. These can be very useful, I like to turn off KVMs, monitors, and other unneeded devices if appropriate.

Keep in mind some server PSUs are active passive, where others are active active. This will effect what happens when they are connected between UPSs.

Sorry I can't directly comment on your question, but isn't that a little underpowered (# of UPSs for existing environment)? How's the runtime? Just curious.

I have a network management card in one of them, it's claiming the current runtime would be 33 minutes. The other unit does not have a NMC (I plan to add one soon) but the load on that one is a bit less. The power here is actually pretty decent, so I'm mostly concerned about short outages and the ability to shut down cleanly. My network equipment is on a separate UPS, just a decent desktop style one.

Tim - switched and managed sounds great, though probably out of my price range. Good to know I'm following the basic idea correctly though, thanks.

You can think of a PDU as nothing more then a glorified power strip that fits in a rack.

How I always set them up is I get two or 4 per rack (depends on the PDU and servers). Then for each I have them powered off their own UPS which in turn is powered off its own circuit. This way I can plug each power supply into its own PDU/UPS/Circuit. Puts a little more redundancy into the mix. :-D

You may wish to run the APC load/run time tools on their website to verify that with the added servers you would not be going beyond the peak power ability of the UPSs.

Keep in mind run time numbers are not reliable. Many UPSs can only generate accurate run time while disconnected form mains. The only true number is a plugs out test.

Also keep in mind loads change at different times, so you need to take peak loads into effect when planning.

Yeah, I think when the power's out it's more like 20 minutes. Still not bad. I'll definitely be putting more thought into it before adding any machines, I was hoping to clean up the wiring first so I'm not compounding the issue. I can always add another UPS and PDU, and get creative from there :)

Rivitir - I keep hoping we move so I can get a more dedicated room. It'd be great to get that detailed about it.

Tim7139 and Rivitir hit it right on the head. PDUs are power strips that can be as basic or as complicated as you'd like. Two thoughts

When you select your PDU (Eaton or otherwise), you should look at PDU accessories to manage your cables. PDU cable managers and a few zip ties go a heck of a long way. Below are some 0U and 1U examples.

If you are planning on using two UPSs for redundant power supplies, make sure that the UPSs are loaded below 50%. This probably isn't an issue for you now, but if you began to grow your rack and went above 50% load - a power supply, PDU breaker, or a UPS failure could take down the whole system as the remaining UPS would be over 100% load. Never a good feeling...

When you select your PDU (Eaton or otherwise), you should look at PDU accessories to manage your cables. PDU cable managers and a few zip ties go a heck of a long way. Below are some 0U and 1U examples.

That picture gives me nightmares. The cables can not be quickly unplugged in an emergency. Even though the unit itself could presumably be unplugged that would be a major violation of the local fire code. Here you can not secure wires within ~6" of the plug or in a manner that would interfere with rapid disconnection. .

I definitely prefer velcro for cable management and try not to use zip ties anywhere anymore - it's too much of a hassle when I need to rearrange or even just add another cable. Still, I can appreciate the organization of those pictures - it's definitely far neater than what I've managed so far.

windso - The more I think about it, the more I think any new servers may just add a third UPS. It'd be a little easier to have two, but these units probably don't have the headroom for too much more.

+1 to Velcro! I built our UPS demo rack and was not happy at all when I had to reconfigure it. Putting my scissors right next to the power and network cables to get the zip ties off... I'm sure you all are more aware of how annoying this can be. We and other manufacturers make PDUs with simple, thin bars right off the PDU instead of plastic pieces so you can still use velcro. Tim7139's comment about code is definitely valid.

And +1 to 220V (208 or 240V)... I am the product manager for Eaton 5-10kVA UPSs and if you can get your equipment running at 208, it is much easier and efficient.

+1 to velcro as well. I always get the long strips of double sided velcro so I can cut my own lengths. Its also typically cheaper since you can get it in bulk.

I also like windso's comment here. I always go for 0U configurations that can be built into the rack. These work by far better and will take very little space in your rack.

When looking at rack replacement I would suggest you look at a power company such as Eaton. I've always found power company racks to have more room and more options for integrating their PDU's and UPS's then computer manufacturer racks.

With this setup, we have racks 1 and 2 going into seperate long power strips I mounted on the wall behind the racks which then each plugs into their own 20A circuits. Rack 3 runs into another power strip on the wall but still doesn't have its own 20A circuit to plug into so that rack is struggling on power and we are splitting out the power to the other power strips for time being until we get the 3rd 20A installed.

With this setup, would it be pretty straight forward to just have about 3 1U PDUs on each rack and have those plug into the 2 20A(soon 3) circuits that are in place? From what I understand of these, the APCs plug into the PDU and the PDU plug into the wall, correct?

The PDU exists to distribute the power coming out of the UPS to connected equipment - so that it can power more devices than there are outlets on the UPS. So, when it's connected in this order, everything connected to the PDU will get UPS protection. All you need to do is make sure nothing gets overloaded, given your unique configuration.

With redundant power-sharing power supplies running from separate sources, you'll need to make sure that neither UPS or mains circuit are ever loaded past 50% so that in a single-UPS or single-circuit failure condition, you can survive the cascading load shift to the UPS or building circuit that's still running as it's called upon to run the entire load.

If you're running power supplies in a combined mode or other non-redundant configuration -- loading the separate circuits and UPS systems up to 100% is no problem.

Answering any questions about how many circuits are required and how you should load them isn't really possible without knowing the measured load values of each device present with an input power cord and whether or not each device is running in a redundant configuration.

Most of us chase UPS recommendations based on an equipment list and work backwards to the PDU, the UPS and ultimately the building circuit size(s). Here you've got 20A mains circuits, but the UPS systems at 1000VA (about 5.5A if SUA1000) and 1500VA (about 8.2A - if SUA1500RM2U) require some fairly involved load balancing to keep stuff from being overloaded.

Sometimes things fall into place a little better by working it backwards by sizing everything to the building circuit -- if you're adding a 20A circuit, get a UPS that can support as much of the 20A as possible. Then connect a 20A PDU to the output of that UPS - but make sure that PDU has a digital amp meter on it. That way, the building circuit, UPS and PDU will be fully loaded all at the same time - and once this happens you can cleanly add additional circuits as your network energy needs grow.

I'm assuming that since you're talking about 1000 & 1500va APC models, that you're working with 120V power. I'm counting 3 20A circuits under discussion here. Things would be a whole lot simpler to monitor and manage if each circuit were protected by a UPS capable of handling the entire 20A circuit (2200VA / 1920 watts minimum) - (in north america, the 80% rule applies, so by code and UL rules - all UPS brands are capped at 16A on their 20A plug-in models).

Then, running a 20A Metered PDU at the output of the UPS and connect your equipment to the PDU. The metered PDU will have a 2 digit LED display showing how many amps are flowing through it. You can then keep track day to day of how much power each of the circuits is supporting -- and know precisely when to add additional capacity to support more equipment as your needs change. When the meter starts to inch closer to 16A, stop adding equipment. If it's a redundant setup with dual UPS systems on dual circuits for each rack, then your max recommended on each UPS/circuit would be 8A.

SAMPLE NON REDUNDANT CONFIG

1. Get a 2200VA UPS (rated as close to 1920w as possible) for each 120V 20A circuit (like this)

1. Get TWO 2200VA UPS systems (1920w) for each PAIR of 120V 20A circuits (a UPS for the "a" circuit / a UPS for the "b" circuit) - (like two of these)

2. Get a 20A metered PDU to connect to each UPS (an "a" PDU plugs to the "a" UPS / the "b" PDU connects to the "b" UPS) - (PDUs like this or this - but this single housing two-circuit PDU where it can do both an "a" & "b" circuit simultaneously)

3. Connect the "a" cord from each device into the "a" PDU and the "b cord from each device into the "b" PDU

You'll have to ensure that the A/B power sources running each device are balanced and that no PDU reports more than 8 amps - so that if you have a solitary failure on either the A or the B line, the PDU/UPS/Circuit that's still live doesn't see more than 16A total.

Providing this type of balance will be a little more complicated if you're looking to keep the 1000 & 1500VA ups systems in service, since they're not able to handle the entire amount or current available on the 20a mains circuits. To prevent the 20A panel breakers from popping, you'll need to ensure that it never sees a load larger than 20A (16A per NEC) - to prevent UPS overload, you'll need to make sure the 1500's never are loaded past 8.2A and the 1000's are never loaded past 5.5A. You can watch the load meters on the front of the UPS systems to ensure you're in-range -- or you could add some 15A metered PDUs so you can view the amp rating continuously at the output of each UPS (you'd have to note somewhere that your drop dead numeric amp value on the 1000 is 5 and the 8 on the 1500 -- (a 120V PDU for each 1000/1500VA ups -like this, or this).

Since this is back from the dead, I thought I'd update what I went with.

First, I added a third UPS, an APC 2200VA. I also installed redundant power supplies in each of my Dell PowerEdge servers, which are my three ESXi hosts. I went with some basic APC power distribution units - no fancy features, but they can handle what I need. My rack is old and doesn't support anything cool, so they're tied on the side. Hopefully if we move next year I can get a real rack :)

There are three PDUs in total, one on each UPS. The three ESXi hosts are the only things connected to the 1500VA units, and they can run for about 30 minutes. Similarly, the third PDU is connected to the 2200VA, and that has two file servers and the switches, also around 30 minutes runtime.

Finally, each UPS got a network management card, so everything gets to shut down clean. I used two foot power cords on everything, so it's all nice and clean in the back.

The entire project came to around $2500 total. It was a lot more than I expected, but shortly after this thread started, we got pounded by tornadoes, which left us without power for a week and resulted in a lot of unhappy servers that didn't get time to shutdown.

The PDU exists to distribute the power coming out of the UPS to connected equipment - so that it can power more devices than there are outlets on the UPS. So, when it's connected in this order, everything connected to the PDU will get UPS protection. All you need to do is make sure nothing gets overloaded, given your unique configuration.

With redundant power-sharing power supplies running from separate sources, you'll need to make sure that neither UPS or mains circuit are ever loaded past 50% so that in a single-UPS or single-circuit failure condition, you can survive the cascading load shift to the UPS or building circuit that's still running as it's called upon to run the entire load.

If you're running power supplies in a combined mode or other non-redundant configuration -- loading the separate circuits and UPS systems up to 100% is no problem.

Answering any questions about how many circuits are required and how you should load them isn't really possible without knowing the measured load values of each device present with an input power cord and whether or not each device is running in a redundant configuration.

Most of us chase UPS recommendations based on an equipment list and work backwards to the PDU, the UPS and ultimately the building circuit size(s). Here you've got 20A mains circuits, but the UPS systems at 1000VA (about 5.5A if SUA1000) and 1500VA (about 8.2A - if SUA1500RM2U) require some fairly involved load balancing to keep stuff from being overloaded.

Sometimes things fall into place a little better by working it backwards by sizing everything to the building circuit -- if you're adding a 20A circuit, get a UPS that can support as much of the 20A as possible. Then connect a 20A PDU to the output of that UPS - but make sure that PDU has a digital amp meter on it. That way, the building circuit, UPS and PDU will be fully loaded all at the same time - and once this happens you can cleanly add additional circuits as your network energy needs grow.

I'm assuming that since you're talking about 1000 & 1500va APC models, that you're working with 120V power. I'm counting 3 20A circuits under discussion here. Things would be a whole lot simpler to monitor and manage if each circuit were protected by a UPS capable of handling the entire 20A circuit (2200VA / 1920 watts minimum) - (in north america, the 80% rule applies, so by code and UL rules - all UPS brands are capped at 16A on their 20A plug-in models).

Then, running a 20A Metered PDU at the output of the UPS and connect your equipment to the PDU. The metered PDU will have a 2 digit LED display showing how many amps are flowing through it. You can then keep track day to day of how much power each of the circuits is supporting -- and know precisely when to add additional capacity to support more equipment as your needs change. When the meter starts to inch closer to 16A, stop adding equipment. If it's a redundant setup with dual UPS systems on dual circuits for each rack, then your max recommended on each UPS/circuit would be 8A.

SAMPLE NON REDUNDANT CONFIG

1. Get a 2200VA UPS (rated as close to 1920w as possible) for each 120V 20A circuit (like this)

1. Get TWO 2200VA UPS systems (1920w) for each PAIR of 120V 20A circuits (a UPS for the "a" circuit / a UPS for the "b" circuit) - (like two of these)

2. Get a 20A metered PDU to connect to each UPS (an "a" PDU plugs to the "a" UPS / the "b" PDU connects to the "b" UPS) - (PDUs like this or this - but this single housing two-circuit PDU where it can do both an "a" & "b" circuit simultaneously)

3. Connect the "a" cord from each device into the "a" PDU and the "b cord from each device into the "b" PDU

You'll have to ensure that the A/B power sources running each device are balanced and that no PDU reports more than 8 amps - so that if you have a solitary failure on either the A or the B line, the PDU/UPS/Circuit that's still live doesn't see more than 16A total.

Providing this type of balance will be a little more complicated if you're looking to keep the 1000 & 1500VA ups systems in service, since they're not able to handle the entire amount or current available on the 20a mains circuits. To prevent the 20A panel breakers from popping, you'll need to ensure that it never sees a load larger than 20A (16A per NEC) - to prevent UPS overload, you'll need to make sure the 1500's never are loaded past 8.2A and the 1000's are never loaded past 5.5A. You can watch the load meters on the front of the UPS systems to ensure you're in-range -- or you could add some 15A metered PDUs so you can view the amp rating continuously at the output of each UPS (you'd have to note somewhere that your drop dead numeric amp value on the 1000 is 5 and the 8 on the 1500 -- (a 120V PDU for each 1000/1500VA ups -like this, or this).

Lots to ponder I know...

Now what would be the con to me doing the PDU and UPS in opposite order? One of my reasons for doing this besides being able to monitor our voltage, is to have less cords running to the wall as we have to move the racks in and out to get access to the back of the rack. Our server room is small so we can't leave the racks in the middle of the room with easy access. We were thinking of having 2 of these 1U PDUs in each rack and have the APC's plug into the PDUs. I don't foresee this immediately pegging out the 20A as the power strips that I have mounted on my wall are only 10A. We had to do some balancing acts to keep them from popping but they are working.

No official "con" to doing it this way, so long as you can keep your loads within tolerance for all UPS, all PDU and all mains circuits. When the total capacity available differs between these 3 devices that are all connected through each other (Circuit Capacity / UPS capacity & PDU capacity), you've got a complicated set of tally's to keep track of to know the limits. When these 3 parts running through each other all have the same rating - it's easier to keep track of things.

Go for it - if you're sure you've got the means to meet the universal rule: Don't overload anything.

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